This invention relates to space filling methods.
In a particular aspect this invention relates to methods for filling pore spaces and fractures in man-made or natural aggregates of minerals or waste material with solid matter for the purposes of lowering permeability, cementing poorly consolidated or unconsolidated materials, or for assisting the disposal and/or stabilisation of various waste materials.
There is a continual need for methods which are capable of filling man-made or natural spaces in a range of settings, such as porous and/or fracture-bearing permeable media.
Such methods can assist with:
permeability reduction for controlling fluid flow (ie. liquid and/or gas) in porous and/or fracture-bearing media,
cementation of poorly consolidated or unconsolidated materials to improve their structural integrity, and
the disposal and/or stabilisation of a range of natural or man-made waste materials.
Permeability reduction methods can be used in a variety of fluid-flow control applications in porous and/or fracture-bearing media. The porous and/or fracture-bearing permeable media may be natural or man-made, underground or above ground, liquid-saturated or gas-saturated. Specific situations may include but are not restricted to the following:
Controlling Fluid-flow in Aquifers
Preventing pollution migration from waste-bearing landfills or other contaminated sites has become an important issue in areas where the groundwater resource has a demonstrated beneficial use. Legislation often requires various types of waste landfills (eg. municipal, industrial or military) or other contaminated sites to be lined with low-permeability natural or synthetic materials which act as pollution containment systems by minimising the outward migration of pollution-bearing fluids, or the ingress of groundwater. At waste disposal or other contaminated sites where no lining has been installed, or where the lining is inadequate or has deteriorated, no low-cost, non-disruptive methods for isolating the waste from the surrounding groundwater are currently available.
Controlling fluid-flow from natural groundwater sources into an open-cut or underground mine can minimise water pollution and the associated costs of treating and/or removing the water. Likewise, real-estate development projects that cause some disruption to the local water table often incur economic penalties as a result of having to handle and/or treat groundwater that is polluted, or that becomes polluted as a result of the disruption.
Controlling fluid-flow in other porous and/or fracture-bearing permeable media:
A range of other man-made and natural porous and/or fracture-bearing media often demonstrate a requirement for permeability reduction methods to control fluid-flow. Such media may include:
Waste-rock Piles at Mine Sites
Filling pore spaces and/or fractures in such bodies of rock waste can exclude incident rainfall and thereby minimise the drainage of acidified or otherwise polluted leachate water from the waste-rock piles.
Dam Walls or Floors, or the Margins of Other Forms of Fluid Containment Systems, Comprised of Geologic or Other Construction Materials
Filling pore spaces and/or fractures, and thereby reducing the permeability of fluid containment systems, can prevent the unwanted migration of fluids through the margins of an impoundment. Few low-cost, non-disruptive techniques are broadly applicable to porous and/or fracture-bearing media in the role of leak-prevention.
Various Types of Porous and/or Fracture-bearing Monuments, Buildings (eg. Foundations) and Other Structures
Reducing permeability by filling pore spaces and/or fractures in the material used to construct some monuments, buildings and other structures can provide protection against chemical attack by preventing infiltration of water (eg. groundwater, surface water or rainwater) and associated dissolved components, or reactive gases (eg. polluted air).
Controlling gas-flow in porous and/or fracture-bearing permeable media:
The flux of air or other gases in man-made or natural media can be controlled by lowering the permeability of the media For example, minimising the flux of air through various geologic strata by filling pores spaces and/or fractures can reduce the amount of oxygen supplied to in-situ, uncontrolled coal fires (located either at the surface or subsurface), and thereby assist with their extinction.
Cementation techniques are designed to improve the binding between adjacent particles in an unconsolidated or poorly consolidated material, and are primarily used to improve the structural integrity of foundation substrates and construction materials during a variety of construction projects, as well as to improve rock stability during mining operations. Existing methods are often expensive, highly disruptive, and either not applicable in some circumstances or relatively ineffective in some circumstances.
Cementation techniques are also used for the repair and/or fortification of monuments, buildings and other structures. The cementation process protects monuments, buildings and other structures by binding the materials and minimising the effects of physical erosion.
New methods are constantly sought to assist with the safe disposal or stabilisation of various types of waste including municipal, industrial, hazardous and military refuse, which may or may not include toxic and/or radioactive substances. Such methods generally have a requirement for providing long-term stabilisation of the waste, whether it is containerised or unbound. Stabilisation infers avoiding unwanted migration of pollutants from the waste which may be brought about by corrosion of containers or deterioration of the low-permeability media surrounding the waste. Space filling methods of the current invention can provide an opportunity to encapsulate man made or natural waste materials or waste-bearing containers in relatively inert, low permeability solid minerals in subsurface (mines, quarries, caves, aquifers . . . etc) or surface impoundments.
Filling the spaces between waste containers or within deposits of assorted waste will reduce the production of leachate, the often polluted liquor generated by the interaction of water and the waste (or waste containers). Encapsulation will minimise the infiltration of surface water or groundwater, and thereby control the interaction of water with the waste or waste container. This method has similarities to the method discussed above for installing a barrier within an aquifer surrounding a landfill or contaminated site. The prime difference being that encapsulating the waste will reduce leachate production, and sealing off an aquifer will minimise leachate migration.
Space filling methods of the current invention may provide a broadly applicable, comparatively non-disruptive, relatively low-cost, multiply repeatable, and often self-sealing process to address the types of issues outlined above, and others not detailed herein. The methods may be applied in-situ to spaces, such as in porous and/or fracture-bearing media, and therefore may be implemented either pro-actively or retroactively.
The present invention provides methods for inducing the precipitation of substantially water insoluble mineral carbonates in pores, spaces and fractures.
by conveying a carbon-dioxide (ie. CO2) bearing gaseous phase or an oxidised-carbon -bearing aqueous phase into spaces where reaction with an existing or introduced fluid phase of appropriate composition occurs, or
by conveying a fluid of appropriate composition into spaces where reaction of the fluid components with a fluid delivery medium occurs, or
by conveying a fluid of appropriate composition into spaces under controlled physical conditions such that unassisted reaction of the fluid components occurs.
The present invention also provides a method of reducing the permeability or improving the structural integrity of natural or man-made aggregates of mineral or waste materials comprising the introduction of carbon dioxide or a soluble carbonate species into the aggregate to react with a chemical compound capable of reacting with the carbon dioxide or soluble carbonate species to form a substantially insoluble carbonate within pores spaces or fractures in the aggregate in broadly controllable geometric distributions,
wherein an appropriate chemical compound capable of reacting with the carbon dioxide or soluble carbonate species to form a substantially insoluble carbonate may need to be introduced to the aggregate if not already present in suitable concentrations or
wherein the carbon dioxide or soluble carbonate species need not be introduced to the aggregate if already present in suitable concentrations.
The present invention also provides a method of reducing the permeability or improving the structural integrity of natural or man-made aggregates of mineral or waste materials comprising the introduction of one or more reactive material to react to form a substantially insoluble carbonate within pores, spaces or fractures.
Space filling methods of the current invention may be applied in a broad range of situations, and the manner in which they are applied will depend on the nature of the setting and the desired outcome. It is unlikely that any given specific application of the space filling technique will be applied in the same fashion at two different locations. However, the general methodology for achieving permeability reduction, cementation or waste stabilisation will be broadly the same.
The following section describes how the technique may be applied to achieve permeability reduction. In the first, a preferred specific methodology for installing a low-permeability cap in the upper portion of an acid generating waste-rock pile is described. The second details how to install a vertical permeability reduction barrier in an aquifer for the purposes of controlling fluid flow.